Re: Explain 3 Phase

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:

> Original poster: "Peter Lawrence by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>
 
> >       (on the 'phase' of the 110/240v:
> >               This seems to ALWAYS lead to confusion, usually
> >               due to semantics, rather than facts.
> >
> >               FACT:
> >                       The two legs are in phase.
> >                       (think about it:  If they were not, there
> >                       would be 0v, not 220v, across the outside...
 
> then why is it that in Op-Amps they use the term "common mode rejection"
> to refer to the "[difference from the expected] zero output voltage" from
> two inputs that are "common" IE "have the same phase" IE "in phase".

	Op amps are not power circuits.
	(hint:
	I have been designing with both for 30 years.
	Commercially....)

> We coilers also use "in phase" to refer to two (or more) NSTs connected
> in parallel such that the voltage between outputs of any two of them is ZERO
> (not the two output terminals of one NST, rather two output terminals of
> different NSTs that you are about to tie together to parallel the NSTs).

	I am aware of this.
 
> You seem to have it backwards from the common use of the term "in phase".

	I don't.
	If they are out of phase, how do they sum to 240 across the
	outside?
 
> What the two legs have in common is 60-Hz, other than that they are 180-
> degrees out of phase.

	Depends on how one interprets the measurement.
	(hint:
	The 110/240 derives from a center tap & two ends from
	ONE TRANSFORMER.  work it out.

> I think you are confusing frequency with phase.

	I'm not....

	Ascii graphics are rough, but:
		________(+110)
		(
		(
		(
		(________neutral
		(
		(
		(
		(________ (-110)

	(secondary only)

	Since the neutral is grounded, the scope reads relative to the
	center, which makes one side LOOK inverted (180 out of phase)

	Again:
	If the two were out of phase, the sum across the outside
	would be 0.

	Hmmmmmmm.  How many here know dot notation, for phasing?
	dot (i'll use a * for visibility) is used to formally show
	instantaneous phase.  Its set by winding direction.:
			*_____________
	________*	(
		)	(
		)	(*____________ (imagine coinnected...asciii graphics)
		)	(
	________)	(
			(______________

	I've omitted cores in all cases....

	best
	dwp